The influence of a live culture of Saccharomyces cerevisiae on the number of ciliates, activity of
carboxymethylcellulose- (CMC), xylan- and starch-degrading enzymes, as well as the concentration
of VFA in the rumen of two cows was examined. The animals were fed either hay and concentrate
alone or supplemented with live yeast given at the rate of 5 g/d. It was found that the response of
rumen fauna to yeast supplementation was related to the animal. The total protozoa and Entodinia
counts increased significantly only in one cow (P≤0.05). The number of protozoa from the genus
Diplodinium remained unchanged (cow 1) or decreased significantly (cow 2). Epidinia decreased
in the rumen of both animals, while Isotrichidae did not change significantly (P>0.05).The activity
of CMC-ase and xylan-degrading enzymes varied between 7.2-9.4 and 108.3-130.0 μM released
reducing sugars/g DM/h, respectively. The effect of yeast on the activity of fibrolytic enzymes was
related to the host animal. CMC-ase decreased significantly only in cow 2, while xylanase, in cow
1. The activities of starch-degrading enzymes as well as pH of rumen fluid and volatile fatty acids
were not affected by supplementation of cows with yeast.

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